Axopatch 200B Current Clamp

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ZVandy's picture
Axopatch 200B Current Clamp

I recently started working with the Axopatch 200B in current-clamp mode (patch).  As a simple test, I checked to make sure that the open circuit (nothing connected to the headstage) reading was 0 mV, but the reading was much larger than 0 mV (greater than 300 mV in some cases).  I restarted the equipment and ran into the same problem.  Based on my understanding, in current clamp mode, the Axopatch 200B uses a feedback circuit to automatically adjust the pipette voltage to keep the pipette current at 0 pA.  If nothing is connected to the headstage, then current cannot be flowing, so I would expect to see a reading of 0 mV since the system does not need to adjust the pipette voltage to keep the current at 0 pA.

Can you think of a reason why I would see a large voltage (>300 mV) V_m reading while everything is disconnected from the Axopatch 200B headstage? 

Thank you in advance for your help.

BigPharmBoy's picture
 Have you tested your open

 Have you tested your open circuit in Voltage Clamp mode?

Switch to voltage clamp mode and make sure that the open circuit doesn't generate any current, i.e. 0 nA. If so, then your 200B is working just fine.

Remember, it's possible to have voltage without current.